spudbean

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jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

rgreenjr

-- show running queries (pre 9.2)
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query 
FROM pg_stat_activity 
WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%' 
ORDER BY query_start desc;

-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query 
FROM pg_stat_activity 
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' 

amitsaha

How does ls work?

I wanted to be really able to explain to a fair amount of detail how does the program :command:`ls` actually work right from the moment you type the command name and hit ENTER. What goes on in user space and and in kernel space? This is my attempt and what I have learned so far on Linux (Fedora 19, 3.x kernel).

How does the shell find the location of 'ls' ?

gubatron

Things to remember when compiling/linking C/C++ software

by Angel Leon. March 17, 2015;

Last update on December 14, 2023

Updated on February 27, 2023

Updated August 29, 2019.

kissgyorgy

from sqlalchemy import create_engine
from sqlalchemy.orm import Session
from myapp.models import BaseModel
import pytest


@pytest.fixture(scope="session")
def engine():
    return create_engine("postgresql://localhost/test_database")

ageitgey

How to install dlib v19.9 or newer (w/ python bindings) from github on macOS and Ubuntu

Pre-reqs:

• Have Python 3 installed. On macOS, this could be installed from homebrew or even via standard Python 3.6 downloaded installer from https://www.python.org/download. On Linux, just use your package manager.
• On macOS:
  • Install XCode from the Mac App Store (or install the XCode command line utils).
  • Have homebrew installed
• On Linux:

akihikodaki

Linux Desktop on Apple Silicon in Practice

I bought M1 MacBook Air. It is the fastest computer I have, and I have been a GNOME/GNU/Linux user for long time. It is obvious conclusion that I need practical Linux desktop environment on Apple Silicon.

Fortunately, Linux already works on Apple Silicon/M1. But how practical is it?

• Two native ports exist.